The present invention relates to a yellow ink composition containing a metal complex pigment, and an ink set using this yellow ink composition, and more particularly relates to a yellow ink composition with high color reproducibility in the high b* and low L* regions in the L*a*b* display system stipulated by the CIE, and an ink set which comprises at least a specified yellow ink, and which is superior in terms of the color reproducibility of recorded images.
Conventionally, the yellow inks provided in ink sets used for color ink jet recording have been inks with a relatively high brightness in order to prevent a state in which dots are visually recognized by the eye in granular form in cases where images are expressed by such dots. For example, high-brightness yellow inks are “high L*, a* close to zero, and high b*” according to the Lab color display system stipulated by the CIE (Commission Internationale d'Eclairage).
When yellow inks that are “high L*, a* close to zero, and high b*” are used, the following problem arises: namely, while graininess is improved, the reproducibility of color with a high b* value is insufficient in the moderate to low brightness region with an L* value (brightness) of approximately 60 or less.
In order to solve such problems, a method has been proposed in which ink sets that are further equipped with a low-brightness yellow ink called “dark yellow” in addition to a high-brighness yellow ink are used (for example, see Japanese Patent Application Laid-Open No. 2002-105368).
Furthermore, a method is also used in which a high b* value is realized in the moderate to low brightness region by increasing the pigment solid content contained in the yellow ink (for example, see Japanese Patent Application Laid-Open No. 2003-313480).
Meanwhile, a method has also been disclosed in which a broad rang of color reproducibility in the yellow region is obtained by means of a yellow ink composition which contains two types of yellow pigments, i.e., C. I. pigment yellow 128 and C. I. pigment yellow 110 (for example, see Japanese Patent Application Laid-Open No. 2001-081369).
However, in the case of methods using dark yellow, the number of ink colors is increased so that ink preparation becomes more complicated, and the cost also tends to increase, and in the case of methods in which the pigment solid content is increased, there are cases in which this leads to a deterioration in luster.
In the case of a method that blends C. I. pigment yellow 128 and C. I. pigment yellow 110, color reproducibility can be obtained over a broader range than is possible in the case of inks that contain only one type of pigment; however, the color reproducibility of dark parts in the yellow region is insufficient. Furthermore, since pigments with widely separated color phase angles are mixed, the saturation of secondary colors tends to drop, and C. I. pigment yellow 110 in particular shows a reddish tinge, so that green shows a low saturation when this pigment is used in the ink set.
Accordingly, it is an object of the present invention to provide a yellow ink composition which is superior in terms of color reproducibility not only in the high-brightness (high-L*) region, but also in the low-brightness yellow region, i.e., the region of “low L*, a* close to zero, and high b”.
Furthermore, it is also an object of the present invention to provide an ink set equipped with a yellow ink which is superior in terms of color reproducibility not only in the high-brightness (high-L*) region, but also in the low-brightness yellow region, i.e., the region of “low L*, a* close to zero, and high b*”.